Technical Field
The disclosure relates to an organic light-emitting diode, and in particular it relates to the composition of a carrier generation layer thereof.
Description of the Related Art
Compared to inorganic compounds, organic compounds are more varied in terms of their material system. Organic materials with any function can be synthesized through the appropriate molecular designs. The films of organic compounds have extremely high flexibility and excellent processability. In recent years, functional organic materials with the above advantages have attracted attention among those in the photonics and electronics industries.
Because organic compounds are inherently free of carriers, they normally have excellent insulative properties. In the electronics field, these organic compounds generally served as insulators, being used in insulation materials, protection materials, encapsulation materials, etc. However, a mechanism wherein a large current flows through organic materials was initially developed in the electronics field. For example, organic films with a total thickness of about 100 nm can be disposed between electrodes. Organic hole transport layers and organic electron transport layers are stacked to constitute a stack of the organic films, and a light-emitting material (phosphorescent material) may serve as an electron-hole combination layer in the stack. By applying a voltage to a device, the electrons and holes can be combined in the light-emitting layer to emit light. As such, the device is a so-called organic light-emitting diode (OLED).
Some related art provides the concept of a carrier generation layer to improve the luminescent efficiency of the OLED, in which an anode, a first electroluminescent layer, a carrier generation layer, a second electroluminescent layer, and a cathode are sequentially stacked. Note that the electroluminescent layer (EL layer) means an organic compound layer, and it may emit light by injecting carriers. In addition, the carrier generation layer is a floating electrode without a connection to an outer circuit.
When a voltage V is applied through the anode and the cathode of the OLED, the carrier generation layer may produce electrons and holes, wherein the electrons are injected into the first EL layer and the holes are injected into the second EL layer. Compared to an OLED with only one EL layer, the OLED with two EL layers may emit double the amount of luminescence using the same current (but using double or higher voltage).
The OLED with the carrier generation layer may enhance the current efficiency and lower the current density several-fold by stacking a plurality of EL layers. Theoretically, the device lifetime should be elongated by the enhanced current efficiency due to lowered current density. However, the selection of the carrier generation material is rare, due to late development. Accordingly, a novel carrier generation material is called for to increase the enablement of the carrier generation material in the OLED.